Cross-linked co-polymers based vinyl monomers such as acrylic acid and/or methacrylic acid provide rheology modification benefits. However, the cross-linking agents commonly used to make these cross-linked co-polymers such as divinyl benzene are highly hydrophobic and not readily soluble in water. Therefore, the cross-linking increases the hydrophobicity of the final cross-linked co-polymer.
The use of lignin-oligomers as cross-linking agents for polymers based on vinyl monomers results in cross-linked co-polymers without the unwanted increase in hydrophobicity. These cross-linked co-polymers exhibit improved solubility.